It has been found that the demands for compact handheld products such as miniature PCs, portable navigation systems, databases, telephones etc. is constantly continually rising. These products require particularly small memories with a high storage capacity and must realize rising switching frequencies and power densities without any problems. In order to be able to meet these requirements, recently use has been made of so-called “chip sandwich constructions.”
In the case of such chip sandwich constructions, chips at the wafer level are stacked to form a 3-D chip system and preferably contact-connected to one another by the production of wire bridges between the individual chips and planes. One example of this is disclosed in JP 2002164499 A and in U.S. Pat. No. 6,703,651, which is incorporated herein by reference. These customary wirings have the disadvantage of high losses and are therefore extremely unsuitable for chips of the new generation having high clock frequencies.
Furthermore, the wire bonding technology is technologically unsuitable for 3-D chip systems because the outlay for producing the wire bridges is considerable and the risk of short circuits between the wire bridges rises as the contact density increases.
In the meantime, chip sandwich structures have become known in which chips are stacked face-to-face, the production of the direct connections between the chips being relatively complicated. For this purpose, firstly a Cu layer having a thickness of approximately 5 μm is applied to the surfaces that are to be connected to one another. Afterwards, the Cu layer is patterned by means of the techniques of standard photolithography, the locations of the interconnections between the two chips being defined. Afterwards, a solder having an extremely small layer thickness of a few microns is applied and the two surfaces are subsequently pressed against one another and connected to one another under the action of temperature. (INFINEON Galaxy, No. 6, Dec. 2002, page 14 “Chip Sandwich revolutioniert Halbleitertechnologie” [“chip sandwich revolutionizes semiconductor technology”]).
In this way, it is possible to realize shorter interconnections between the chips, thereby enabling clock frequencies in excess of 200 GHz. However, the outlay for realizing these interconnections is considerable owing to the required photolithography.
It is thus necessary to develop a novel connection technology in order to be able to produce the interconnections between chip sandwich arrangements more cost-effectively and more effectively.